Structural and electronic transport properties of polycrystalline ZnO thin films, prepared by pulsed laser deposition, have been investigated. The films were deposited on glass and Si3N4/Si substrates using O2 and N2 atmospheres. X-ray analysis revealed preferential c-axis orientation perpendicular to the sample substrate. Films deposited under relatively high O2 pressure were highly resistive. However, the conductivity σ increased while the films were irradiated with ultraviolet light, showing an Arrhenius (In σ ∝ T-1) dependence as a function of temperature. The ZnO film deposited in N2 atmosphere exhibited at room temperature a resistivity ∼ 1 Ω cm, and a sheet carrier concentration ∼ 5 1012 cm-2. The variation of the conductivity with temperature, in the range 60 – 150 K, follows a In σ ∝ T-1/4 dependence characteristic of variable range hopping. An analysis of the experimental results of conductivity as a function of temperature, in terms of possible doping effects, as well as conduction mechanisms is presented.